Material for sound-absorbent and heat-insulating lining of an automotive engine compartment

ABSTRACT

The invention relates to a moulded part which can be used as a sound absorbent and heat insulating lining for an automotive engine compartment. Said moulded article consists of a carbon-fiber heat insulating layer (1) facing the engine compartment, a rear thermoplastic-fiber supporting layer (2) and a sound absorbent insert (3). Heat insulating layer (1) and supporting layer (2) are designed as a non-woven knitted fabric comprising a stitched layer which binds all fibers and is made of flatly disposed stitches, and a looped protruding pile layer. Stitched layers (4,4&#39;) of heat insulating layer (1) facing engine compartment, and rear supporting layer (2) define the outer surface of the material. Supporting layer (2) is moulded by hot pressing to form a dimensionally stable moulded part.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of PCT applicationPCT/EP97/05607 filed Oct. 10, 1997 with a claim to the priority ofGerman application 196 42 714.2 itself filed Oct. 16, 1996.

FIELD OF THE INVENTION DESCRIPTION

The invention relates to a material for sound-absorbent andheat-insulating lining of an automotive engine compartment. The materialis formed into a molded part and usable as a rigid wall element, housingelement, or the like.

The material is mounted in the engine compartment of a motor vehicle andis intended to reduce sound and heat emissions as much as possible. Itis mounted on the firewall between the engine and passenger compartmentsand can also be mounted on the underside of the hood and can be used toencapsulate the engine. The material must be sufficiently heat resistantto withstand the temperatures produced by the vehicle and also benonflammable, and have a surface that is water- and oil-shedding, aswell as resistant to dirt. Of course it also must have limited thermalconductivity and the ability to absorb considerable sound.

In practice glass fibers are added to the fleeces stabilized for thenamed purposes with phenolic resins with the hot front side beingcovered with a fleece of glass fibers. The surface weight of the knownmotor-compartment lining is considerable and the heat-insulatingcapacity as well as the sound-absorbing capacity could be improvedrelative to the amount of material used.

German 4,114,408 describes a textile damping material that is made of apile fleece knit which is formed of a stitch layer holding all fibersand formed of flat stitches as well as upstanding loops. Glass fibersare inserted and also fiber mixtures of glass fibers and carbon fibersare possible. The material is voluminous and one side of the materialhas a terry or plush-like structure that holds dirt and which can onlybe adhered with difficult to body parts. It cannot be made rigid for useas a structural part.

Similarly German 4,125,351 describes a textile damping material that isformed of two fiber layers that each have a stitch layer and a layer ofupstanding loops. The stitch layers are arranged on the outer faces withthe loops forming an intermediate cushion. One layer of fibers can bemade of carbon fibers and the other layer can be of natural or syntheticfibers. The material is voluminous and has good heat-damping capacity.Its sound absorbency, in particular the absorption of body noises, isunsatisfactory. As a result of the inadequate sound-absorbing capacitythe material is also not suitable for the above-described application.Even this material cannot be made stiff for structural use.

It is an object of the invention to provide a material for the sound-and heat-absorbent lining of the engine compartment of a motor vehiclethat has a high heat-insulating capacity, is heat-resistant, that has adirt-resisting surface, that can easily be used as a structural part inthe engine compartment, and whose sound-absorbing capacity is suitablefor this use. The material should according to application reduceemission of body sounds and/or air sounds considerably.

The invention and solution of this object is a material forsound-absorbent and heat-insulating lining of an automotive enginecompartment comprising

a heat-insulating layer of carbon fibers turned toward the enginecompartment,

a rear carrier layer, and

at least one sound-absorbing core layer, the heat-insulating layer andthe carrier layer each being formed of a pile fleece knit which has astitch layer of flat stitches holding all fibers as well as a pile looplayer of upstanding cushion-forming loops, the stitch layer which formsthe heat-insulating layer turned toward the engine compartment and theback carrier layer which forms the outer faces of the material and thecarrier layer being formed of thermoplastic fibers and being formable byhot pressing into a structurally stable body. The stitch layer of theheat-insulating layer preferably has oil- and water-repellingproperties.

The carbon-fiber heat-insulating layer has considerable heat resistance.The pile loops, which can have a height of 10-20 mm, form a cushion withconsiderable heat-insulating properties. As a result of the highheat-insulating capacity of the carbon-fiber heat-insulating layer thematerials for the carrier layer and the core layer can be selectedfreely. The material and formation of the carrier layer as well as ofthe core layer are selected according to application. The selection ismade so that the sound absorbency is increased so that as a result ofthe material selected and its construction body sounds and/or air soundscan be selectively reduced. Hot pressing of the thermoplastic-fibercarrier layer forms a structural part that can be used as a rigid shelland for example as a deflector wall, housing half for a motor, or thelike. Possibilities of further formations are described more closely inthe following.

It is within the scope of the invention that the stitch layer of theheat-insulating layer lies on the pile loops of the back carrier layerand the loops of the heat-insulating layer is mounted on the stitchlayer of the back carrier layer and the loops extend through the corelayer.

Another embodiment of the invention is that the loops of theheat-insulating layer and the rear carrier layer end at and are stitchedinto the core layer. The material, thickness, and weight of the corelayer can be freely selected. According to a preferred embodiment thecore layer is formed of body-sound-absorbing needle felt or amechanically stabilized fleece, e.g. of cotton card fibers, and has alayer density that is greater than the density of the pile-fleece knitsit is sandwiched between. The result is a particularly voluminousmaterial with very good heat- and sound-insulating properties ascompared to the above-described systems.

With all the above-described embodiments the core layer can be abody-sound-absorbing needle felt, a mechanically stabilized fleece, andthe like. It is further possible according to the invention to use apile-fleece knit which has upstanding pile loops and a layer of coplanarstitches holding all the fibers of the core layer, the stitch layer ofthe heat-insulating layer lying on the pile loops of the core layer andthe pile loops of the heat-insulating layer as well as of the carrierlayer being worked into the stitch layer of the sound-insulating layer.This embodiment is ideal when the least possible air-sound emissions arerequired.

The core layer can be made of many types of fibers. Preferably cotton,aramide, heat-resistant polyester, and mixtures of these fibers areused. Cotton fibers improve the acoustic performance of the material;aramide fibers and heat-resistant polyester fibers are recommended whenvery high temperatures are being encountered and a particularly highheat-insulating capacity is required.

The invention is described more closely in the following with referenceto a drawing showing only one embodiment.

FIGS. 1 to 4 schematically show a longitudinal section through amaterial for sound-absorbent and heat-insulating lining of an automotiveengine compartment in various embodiments.

FIG. 5 shows with comparative measurements the sound-absorption capacityof the material according to the invention.

FIG. 6 shows in perspective view a portion of a hot-pressed structuralpart of the material according to the invention.

The material shown in the figures consists of a carbon-fiberheat-insulating layer 1 turned toward the engine compartment, a backcarrier layer 1 of thermoplastic fibers, and at least onesound-insulating layer 3. The heat-insulating layer 1 is formed of apile-fleece knit which has a stitch layer 4 of flat stitches holding allcarbon fibers and a pile loop layer formed of upstanding cushion-formingpile loops 5. The stitch layer 4 is provided with an oil- andwater-shedding additive. Such oliophobic and hydrophobic coating agentsare known.

The carbon-fiber heat-insulating layer 1 is characterized by a hightemperature resistance and has as a result of the cushion 6 formed bythe pile loops 5 good heat-insulating capacity. This makes it possibleto freely select the material and construction of the sound-absorbinglayer 3 as well as of the carrier layer 2 and to adjust them dependingon application. The back carrier layer 2 is formed as a pile-fleece knitwhich has a stitch layer 4' of flat stitches holding all fibers of thecarrier layer 2 and a pile-loop layer formed by upstanding pile loops5'. Thus the stitch layers 4 and 4' form outer surfaces of the materialon the heat-insulating layer 1 turned toward the engine compartment andon the back carrier side 2. These surfaces are smooth, not likely tocatch dirt, and can easily be secured to the vehicle body. Manypossibilities are available for the core layer 3.

In the embodiment of FIG. 1 the stitch layer 4 of the heat-insulatinglayer 1 on the pile-loop layer of the back carrier layer 2 and the pileloops 5 of the heat-insulating layer are worked into the stitch layer 4'of the back carrier layer 2. The pile loops 5 and 5' extend through thecore layer 3.

FIG. 2 shows a similar embodiment. The core layer 3 lies on the stitchlayer 4' of the back carrier layer 2 and is traversed by the pile loops5 formed of carbon fibers of the heat-insulating layer 1 turned towardthe engine compartment.

In the FIG. 3 embodiment the pile loops 5 and 5' define theheat-insulating layer 1 and the back carrier layer 2 in the core layer 2and are enmeshed in the core layer 3. The core layer 3 of theembodiments of FIGS. 1 to 3 can comprise a body-sound-absorbing needlefelt or a mechanically stabilized fleece material. Good sound insulationis in particular obtained with a core layer 3 of cotton fibers. In theembodiment according to FIG. 3 the thickness of the core layer 3 canvary widely. According to a preferred embodiment the core layer 3 isformed of a mechanically stabilized fleece of cotton card fibers and hasa thickness between 10 and 25 mm. The pile-fleece knits on both sidesare thinner and have a thickness of about 5 mm.

In the embodiment of FIG. 4 the core layer is a pile-fleece knit whichhas a stitch layer 4" of flat stitches holding all the fibers of thecore layer 3 and upstanding pile loops 5", the stitch layer 4 of theheat-insulating layer 1 lying on the pile loops 5" of the core layer 3and the pile loops 5 and 5' of the heat-insulating layer 1 and of thecarrier layer being worked into the stitch layer 4" of the core layer 3.The pile-fleece knit forming the core layer 3 consists in thisembodiment of heat-resistant aramide fibers and/or temperature-resistantpolyester fibers or a mixture of these fibers.

FIG. 5 shows the results of comparative measurements between a materialA according to the invention not hot-pressed into a structural part withthe construction shown in FIG. 3, of an insulating material B accordingto German 4,125,351, an insulating material C according to German4,114,408, and a mechanically stabilized cotton fleece D. The comparedmaterials had the same physical strengths. The degree of soundabsorption according to frequency of the sound waves is shown. Thematerial A according to the invention has a significantly better degreeof sound absorption as the known insulating materials B to D. Theimprovement is particularly significant in the higher frequency range.

The carrier layer 2 consists of polyester fibers. The carrier layer 2 ishot pressed into a structural part which can be used as a rigid shell,for example as a spray wall, housing half shell for a motor, or thelike. FIG. 6 shows a structural part for the inner face of the hood of amotor vehicle. The structural part is a rigid body and has a shapecorresponding to the vehicle hood.

What is claimed is:
 1. A material for sound-absorbent andheat-insulating lining of an automotive engine compartment comprisingaheat-insulating layer of carbon fibers for placement adjacent the enginecompartment, a rear carrier layer and at least one sound-absorbing corelayer, the heat-insulating layer and the carrier layer each being formedof a pile fleece knit which has a stitch layer of flat stitches holdingall fibers as well as a pile loop layer of upstanding cushion-formingloops, the stitch layer which forms the heat-insulating layer forplacement adjacent the engine compartment and the back carrier layerwhich forms the outer faces of the material and the carrier layer beingformed of thermoplastic fibers and being formable by hot pressing into astructurally stable body.
 2. The material according to claim 1 whereinthe stitch layer of the heat-insulating layer has oil- andwater-repelling properties.
 3. The material according to claim 1 whereinthe stitch layer of the heat-insulating layer lies on the loops of theback carrier layer and the loops of the heat-insulating layer is mountedon the stitch layer of the back carrier layer and the loops extendthrough the core layer.
 4. The material according to claim 1 wherein theloops of the heat-insulating layer and the rear carrier layer end at andare stitched into the core layer.
 5. The material according to claim 1wherein the core layer is formed of body-sound-absorbing needle felt. 6.The material according to claim 1 wherein the core layer is formed of amechanically stabilized fleece of cotton card fibers.
 7. The materialaccording to claim 1 wherein the core layer is a pile-fleece knit whichhas upstanding pile loops and a layer of coplanar stitches holding allthe fibers of the core layer, the stitch layer of the heat-insulatinglayer lying on the pile loops of the core layer and the pile loops ofthe heat-insulating layer as well as of the carrier layer being workedinto the stitch layer of the sound-insulating layer.
 8. The materialaccording to claim 7 wherein the pile-fleece knit of the core layer ismade of aramide fibers, heat-resistant polyester fibers, cotton fibers,or a mixture of these fibers.
 9. The material according to claim 1wherein the carrier layer is formed of polyester fibers.